Do boy’s and girl’s cerebral hemispheres develop at different rates ?

Read Also

An intriguing model of a sex difference in the cerebral hemispheres of humans has been principally articulated by  the neuropsychologist Jerre Levy.  Insightfully,  she has argued that the ensemble of sex differences in cognitive abilities do not support a notion of a full left hemisphere superiority of women nor of a full right hemisphere superiority of men.    Instead,  she has proposed that the fetal and infant boy’s right hemisphere develops more quickly than that of the girl,  whereas the girl’s left hemisphere develops more quickly than the boy’s.  Levy seems to be speculating about the right and left hemispheric cortex,  though she does not state so explicitely.  Evidence for a precocious right hemisphere cortical advantage for boys includes the following. One study looked at 3 year old infant’s evoked potentials to auditory stimuli.  The boys had a right hemisphere dominant response whereas the girls had a left hemisphere dominant response.  Similar sex differences in evoked potential topography have been obtained using music, noise, clicks, or speech as stimuli.   Maturation of the hemisphere protects against a form of infantile epilepsy called febrile convulsion.  In short,  there is only a short time period during which febrile cionvulsions can occur,  thus providing an interesting test of asymmetry of hemispheric development.   Post-convulsive hemiplegia (paralysis of one side of the body due to damage to the contralateral hemisphere) reveals that boys more often show evidence of left hemisphere damage,  presumably because of a developmental lag of that hemisphere.   Boys show a left hand advantage in reading braille and in discriminating shapes,  whereas girls show the opposite advantage.   Other sex differences have been reported though (not considered by Levy) which argue against faster right hemisphere development in boys.

Levy has not,  to my knowledge,  been clear on what she thinks happens after puberty to the hemispheric cortices.  Do they settle into asymmetries which are more or less sexually dimorphic ?  What happens to performances on the same tasks used with the children:  do they become more symmetrical ?  Does the sex difference disappear  ?  This model seems worth testing to me.   Much careful developmental research will have to be carried out to validate it.   The first thing that needs to be done is a careful postmortem analysis of human brains (especially of cortical brain tissues) of children and adults of all ages and of either sex.  Christine DeLacoste has reported that the human fetal left frontal lobe develops faster than the right in females but not in males.  Though this finding vaguely supports Levy’s thesis,  much more work needs to be done.  Then the behavioral concommittants expected from the evolving sex differences (if such differences exist) will have to be tested across the life span using the same tests throughout. My own understanding of the relevant developmental literature suggests to me that a) neonates have virtually no cortical function,  making the issue of perinatal hemispheric cognitive specialization nearly irrelevant, b) both male and female preschoolers do develop left hemisphere specialization for language and right hemisphere specialization for spatial analysis,  but this specialization remains very weak, most often insignificant until school age, and c)  whatever sex differences which have been observed in lateralized behavior in preschoolers are so rare, and those that have been observed are so subtle, that they do not suggest any important underlying sex difference in anatomical development of the whole hemispheres.   At most,  some parts of the hemispheres, including parts of the cortical mantle, might manifest some specific sex differences which could change during development.